Speaker magnet having curved preferred direction of magnetization



R. J. PARKER Dec. 22, V1970 SPEAKER MAGNET HAVING GURVED PREFERRED DIRECTION 0F MAGNETIZATION Filed March 14, 1969 I Qww 4 o /NVENTOR ROLLIN J. PARKER A rToR/VEV United States Patent O SPEAKER MAGNET HAVING CURVED PRE- FERRED DIRECTION OF MAGNETIZATION Rollin J. Parker, Greenville, Mich., assignor to General Electric Company, a corporation of New York Continuation-impart of application Ser. No. 515,401,

Dec. 21, 1965. This application Mar. 14, 1969,

Ser. No. 807,390

Int. Cl. H01f 7 00 U.S. Cl. 335-231 6 Claims ABSTRACT OF THE DISCLOSURE A permanent magnet has a preferred direction of magnetization along a curved path, one end of which intersects a side surface of the magnet and another end of which intersects an end surface of the magnet. Magnets with such a direction of magnetization are particularly useful in speaker structures for concentration of the magnetic flux at the air gap. Such magnets permit speaker structures of increased effectiveness, particularly by use of an inexpensive annular pole piece or by use of multiple diameter magnets.

This application is a continuation-in-part of my copending application S.N. 515,410, filed Dec. 2l, 1965, Now U.S. Pat. 3,440,364.

This linvention relates to permanent magnets and permanent magnet assemblies for use in speakers and to a process for the production of such magnets.

My aforementioned copending application, S.N. 515,- 401, discloses a permanent magnet having a preferred direction of magnetization along an axially disposed curved path which intersects the side surfaces of the magnet. Such a direction of orientation concentrates the magnetic flux so that the magnet is particularly effective in speakers because the flux is concentrated at the air gap. The present invention deals with a modification of the concept there disclosed in that the preferred direction of magnetization is along an axially disposed curved path, one end of which intersects a side surface of the magnet, and a second end of which intersects the end of the magnet. The permanent magnets of the present invention are of greatest value with larger voice coils, where the length-todiameter ratio of the magnets is normallyless than that with smaller coils due to the load requirements of the gap permeance, and particularly where the length-to-diameter ratio of the permanent magnets is below 1.0. The invention results in a number of advantages over conventionally oriented magnets. It permits design modifications in speaker assemblies which produce speakers of increased effectiveness, particularly in those instances where larger voice coils are used.

The process of orienting the permanent magnets of the present invention is substantially the same as that disclosed in the aforementioned parent application. A pair of permanent magnets of the present invention placed back to back together possess the same orientation path as a single permanent magnet of the parent application. Thus the present magnets are oriented in the same manner as those of the parent application, except that the magnets are oriented in pairs rather than sin-gly.

The invention will be more clearly understood from the following description taken in connection with the accompanying drawing in which:

FIG. 1 is an elevational sectional view of a cylindrical speaker magnet of the invention showing the manner of its orientation,

FIG. 2 is a sectional view of a permanent magnet as- ICC sembly of the invention comprising a return-path element and a permanent magnet,

FIG. 3 is a plan view of the assembly of FIG. 2,

FIG. 4 is a sectional view of an alternative permanent magnet assembly of the invention comprising a returnpath element and a dual-diameter magnet, and

FIG. 5 is a sectional view of an apparatus suitable for orienting permanent magnets in accordance with the invention.

As can be seen in FIG. 1, a cylindrical speaker magnet 1 having end surfaces 2 and 3 at opposite axial extremities and a side surface 4 is oriented so that its preferred direction of magnetization is along a curved or arcuate path 5 disposed symmetrically around the axis AA of the permanent magnet 1. It will be noted from FIG. l that the curved path 5 intersects the side surface 4 of the magnet at 6 along the top portion of the magnet and at 7 along end surface 3 of the magnet. Thus, a first pole will be created along one extremity of a side surface of the magnet at 6, and a second pole will be created on the end surface of the magnet at 7. The path of preferred magnetization shown in section in FIG. l extends symmetrically completely about the axis of the permanent magnet. The path of orientation is therefore described by rotating curve 5 through a complete 360 arc about the axis AA of the magnet. Any plane passing thru the central axis of the magnet would produce the orientation path shown in section in FIG. 1.

A magnet oriented as shown in FIG. 1 will concentrate the magnetic flux in the region of the voice coil travel and thus produce increased magnetic circuit efliciency in conventional speaker circuits using either cup type return paths which completely surround the magnet or strap type return paths which are open at the sides. However, the invention also makes possible certain unique circuit designs, two of which are illustrated in FIGS. 2-4 of the drawing.

FIGS. 2 and 3 show, in cross-sectional elevation and plane respectively, a permanent magnet assembly coinprising a cylindrical permanent magnet 10 situated concentrically within cup-type return-path element 11. The return-path element surrounds said permanent magnet 10 and forms an air gap 12 along a first pole of the magnet. An annular lL-shaped pole piece 13 is placed on the top of the permanent magnet at the air gap. The length of leg 14 of said pole piece is greater than the corresponding dimension of the adjacent portion 15 of the returnpath element at the air gap. Pole piece 13 will thus collect the linx over a wide annular path and concentrate the flux density level at the air gap as the iiux crosses the air gap into the adjacent portion of the return-path element.

The pole piece 13 may consist of an inexpensive lowgauge steel punching. Thus, at low cost, edge fiux is collected and concentrated at the air gap. This arrangement is particularly useful, for example, for high-frequency tweeters where it is desirable to concentrate and localize the magnetic energy in a relatively narrow region. This design diminishes leakage and localizes the flux into a relatively narrow band. It also serves to decouple the magnet fromthe voice coil and reduce the magentic dirt problem, of much concern in building reliable speakers.

FIG. 4 illustrates another embodiment of the invention in which a permanent magnet-return path assembly utilizes both a conventional magnet and a magnet oriented as here disclosed. Best speaker response is achieved where the diameter of the voice coil is kept as small as possible. This of course acts as a limitation on the diameter of the magnet that may be used at the air gap. In the embodiment shown in FIG. 4, magnetic energy is supplied by seperate permanent magents 20 and 21. Smaller-diameter magnet 20 is oriented in accordance with the practice of the invention. Larger-diameter magnet 21 may be a conventional magnet with usual axial orientation. The magnetic circuit of the permanent magnet assembly shown in FIG. 4 is completed by the return path element 22 which forms, together with permanent magnet 20, an air gap at 23. In this embodiment, magnet of the invention replaces a conventional soft steel pole piece and serves the dual purpose of energy source and energy concentrator. Ideally, smaller magnet 20 at the air gap should have the highest possible induction and should be driven to a high loading level by the larger magnet 21 below it. The bulk of the magnetic energy should be supplied by the larger magnet, as it is not space-.limited as is the magnet at the air gap. Because performance close to the voice coil is induction-limited, the smaller magnet is preferably a high-induction magnet possessing a so-called directional grain or columnar structure. The larger magnet may be either directional or nondirectional grain, depending on performance requirements and cost considerations. Directional-grain magnets are produced by extracting a major portion of the heat of solidification of the molten alloy from only one end by means of a metal chill. This process produces magnets having long columnar crystals extending lengthwise of the magnet. They are disclosed more fully in Ebeling U.S. Pat. 2,578,407.

The dual-diameter permanent magnet shown in the permanent magnet assembly of FIG. 4 may consist of two individual magents as illustrated, or, alternatively, the magnet may consist of a single multiple-diameter unit. If it consists of separate magnets, the design and unit properties of the magnets would, of course, have to be integrated to provide the required performance characteristics in the speaker. If the two magnets are a unitary structure, it may be made as a one-piece casting, with columnar properties at one end in accordance with known practice but with the preferred path of orientation curved in accordance with the invention in that portion of the magnet having the smaller diameter.

The permanent magnets of the invention my be oriented along the curved preferred direction -by apparatus illustrated in FIG. 5. Such apparatus includes a ceramic tube 24 containing permanent magnets 25-32, which may, for example, be cast Alnico 5. Soft iron washers 33-37 at the juncture of every second permanent magnet act as pole pieces. An outer cylindrical tube 38 of any magnetically permeable material, such as soft iron, surrounds the entire structure and acts as a return-path element. The outer tube 38 is wound in periodic fashion by windings 39, 40, 41 and 42 to create a series of poles of 25 and 26, an opposite direction around next adjacent magnet. Thus, it is wound in a first direction around magnets 25 and 26, an opposite direction around next adjacent magnets 27 and 28, the first direction again around magnets 29 and 30, and so forth, to create alternating north and south poles surrounding abutting end portions of each pair of permanent magnets. As can be seen in FIG. 5, this arrangement permits magnetic flux to flow from washer 33 thru an arcuate or curved path thru cylindrical magnets 25 and 26 to an opposite pole at next successive washer 34, thru the return path element 38 to repeat the circuit. The circuit would, of course, be repeated throughout the orientation device.

By arranging any number of such periodic fields around the thermally insulating, temperature-resistant tube 24 containing the speaker magnets, a number of such magnets may be oriented in accordance with the teachings of this invention. The permanent magnets are first heated to a temperature above their Curie temperature, and preferably about 300 C. above their Curie temperature, and then cooled thru the Curie temperature to room temperature in accordance with a prescribed cooling cycle, while the magnets are subjected to a magnetic field in the foregoing apparatus. The cooled magnet will be oriented along the curved path described above. The process is identical to that described in my aforementioned parent application S.N. 515,401, except that the magnetic flux of each circuit flows through a pair of magnets rather than through a single magnet.

I claim:

1. A multiple-diameter permanent magnet having end surfaces and a side surface therebtween extending along the axis of the magnet,

a first portion of said magnet adjacent one end thereof having a first diameter, a second portion adjacent the opposite end thereof having a diameter larger than the first portion,

the magnet having a first pole around a side surface of the first portion and a second pole at the end surface of the second portion, the preferred direction of magnetization lying along a curve disposed about the axis of the magnet and connecting the first and second poles.

2. The permanent magnet of claim 1 in which the magnet is composed of Alnico 5 magnetic material.

3. The permanent magnet of claim 1 in which the first portion of the magnet is of directional-grain columnar structure.

4. The multiple-diameter permanent magnet of claim 1 in which the first and second portions of the magnet are separate cylindrical units placed physically contiguous to each other.

5. A permanent magnet assembly comprising:

the multiple-diameter permanent magnet of claim 1,

and

a return path surrounding said multiple-diameter permanent magnet and forming an air gap therewith adjacent the side surface of the first portion of said magnet.

6. A permanent magnet assembly comprising:

a permanent magnet in the form of a cylinder, said permanent magnet having end surfaces and a side surface therebetween extending along the axis of the magnet, said permanent magnet having a first pole around a side surface of the permanent magnet and a second pole on an end surface of the permanent magnet, the preferred direction 0f magnetization lying along a curve disposed about the axis of the magnet connecting the first and second poles,

a return-path element surrounding said permanent magnet and forming an air gap therewith along the first pole of said magnet at the side surface thereof, and

an annular L-shaped pole piece placed on said permanent magnet with a. leg thereof surrounding said first pole at said air gap, said leg being longer with the adjacent portion of the return path element at said air gap.

References Cited UNITED STATES PATENTS 1,997,193 4/1935 Kato et al. 252-6256 2,380,616 7/1945 Snoek et al. 164-57 2,652,925 9/1953 Vermeiren 335-284X 3,168,686 2/1965 King et al. 335-306 3,176,086 3/1965 Coen 179-119 3,240,882 3/1966 Eichler 179-1 19X 3,326,610 6/1967 Baermann 335-306X 3,247,331 4/ 1966 Cunningham 179-117X OTHER REFERENCES Japanese patent publication, No. 35/ 17,352.

G. HARRIS, Primary Examiner U.S. Cl. XR. 148-103; 179-117 P04050 UNITED STATES PATENT OFFICE (5/69) CERTIFICATE OF CORRECTION Patent No. 3,550,7051 ,pared December 22, 1970 {FHL} i'.

Inventor(s) Rollin J. Parker u It iscetified that error appears in the above-identified pate 'and that said Letters .Patent are hereby corrected as shown below:

. lIn the "Specification: i A

Column 2, ].`:.ne`60, cancel "magentc" and insert magnet column 3, -line 5o, Cancel -25 and 26, ail oppoSi--dircti around next adja'cent" and insel:

oposte pol- 'arity at the extremities of every second-u 1n the 4.claimszlA 

